The smaller and more even the particle size of the baked material, the more quickly and uniformly it can be cooled. This has a favourable effect on the size of the cooler and the quality of the product. The connection of a crusher for crushing the baked material upstream of the cooler and directly following the furnace has therefore already been considered (DE-A 29 25 665). The service life of the crusher is primarily dependent on its effective temperature load. The latter is determined on the one hand by the intensity of the transfer of heat from the material to components of the crusher which are subject to wear, and on the other hand by the cooling of those components. This load is the lower, the shorter the time of contact between the crusher components and the hot material and the more freely cooling air can be passed through the crusher. From these points of view consideration has been given to percussion impact crushers (FRA-2 194 133, DE-C 33 23 565, DE-A 29 25 665), an autogenous mill (DE-A 29 25 665), air-swept mills DE-B 23 61 060 ), drop impact crushers (DE-A 35 26 345) and roll crushers (DE-B 27 47 732). When these crushers have active crushing elements, the latter are distinguished in that they rotate and that they are in contact with the baked material only during a small part of their revolution and can be intensively swept over by cooling air during the remainder of their revolution.
Jaw crushers, which are known per se (EP-A-0 148 780, WO-A-85 03 887, SU-782 860, DE-C 266 524), have not hitherto been used for hot material because they do not provide these favourable preconditions for hot operation. On the contrary, the surfaces of the crushing elements are continuously in contact with the hot baked material even when no impulse exchange takes place. As the crushing chamber is filled with material to be crushed, said surfaces are scarcely accessible to a flow of cooling air.
It is thus contrary to previous views that for the purpose of reducing manufacturing and operating costs of the crusher working under hot conditions that the invention proposes a jaw crusher.
The invention has however realized that a jaw crusher arranged in the manner indicated can have advantages over other types of crushers for the following reasons: whereas at temperatures of 1000.degree. to 1500.degree. C. in the latter the crushing elements are subjected to a combination of thermal stress, particularly also temperature change stress, and high specific impact stress while undergoing a rubbing relative movement, in the case of the jaw crusher practically no temperature change stress occurs because both the heat transfer from the material and the cooling action are practically invariable over a period of time, so that protective elements of heat-resistant metal alloys or ceramic materials can be used for the crusher jaw surfaces subjected to stress. Whereas the crushing tools of rotary crushers are practically inaccessible to cooling from the side remote from the material to be crushed, jaw crushers can be more effectively cooled because their entire rear surface, that is to say a surface which is exactly as large as the surface participating in the crushing operation, is available for the introduction of cooling power. The increased thermal stressing of the crushing jaw surfaces through intensive contact with the material to be crushed can thus be effectively countered by the installation of cooling devices in the crushing jaws. The specific impact stress, which in the case of types of crushers rotating at high speed is determined by the relative speed of the crushing elements and the mass of the pieces of material to be crushed, is low in the given case of use for jaw crushers because at the high temperature the material has no substantial hardness.
It has in addition been realized that a jaw crusher is insensitive to the ejection of material from a rotary tubular furnace in an irregular manner over a period of time. Its crushing chamber, which widens in funnel fashion in the upward direction, can easily be made so large, in respect of crushing chamber size and geometry of the crushing mouth, that it can also deal with the greatest fluctuations of the stream of particles and ejection rate to be expected in normal furnace operation, without requiring an intermediate storage space (for example a feed hopper), which under the difficult conditions would have a tendency towards bridge building and caking. The crushed bulk material is discharged through the outlet gap which is situated in the bottom part of the crushing chamber and the width of which is adjustable to a predetermined final particle size of the bulk material.
The fraction of the product particle range entering the crusher with a particle diameter smaller than the width of the outlet gap flows through the crushing chamber without being included in the crushing process, so that no additional superfine particles are produced. By means of a preferably profiled configuration of the stressing surfaces of the crushing jaws and because of the short residence time of the coarse material in the crushing chamber during the crushing operation, the particle range of the material is evenly distributed over the outlet cross-section.
It is thus found that jaw crushers provide a number of unexpectedly good properties for this application, which justify the inventive merit of this selection. However, as a rule the crushing jaws are provided with cooling devices. These may be cooling air-swept ducts which extend through the crushing jaws and lead into the crushing chamber in order to cool not only the crushing jaws but also in particular the material to be crushed. This is expedient when the crushed material tends to sinter together or cake. To ensure that the mouths of the cooling ducts are not clogged by the material to be crushed, they expediently extend downwards under imbricated protective elements, their mouths being protected against the material pressure directed essentially at right angles to the crushing jaw by their arrangement under or behind the downwardly pointing end face of the respective protective element. If it is not necessary for the material which is to be crushed to be itself cooled, internal cooling of the crushing jaws is sufficient, for example by means of coolant ducts. extending parallel to the stressing surface in the crushing jaws.
By means of adjusting devices installed in the cooling air supply and/or distribution ducts, the local intensity of the cooling of the crushing jaws and of the blast of air into the crushing chamber can be adjusted.
The crusher is generally installed in the duct which is disposed between the furnace and the cooler and which conducts the material downwards and the hot air preheated by cooling upwards to the furnace as secondary air. Because of this dual function, the crusher must not fill the entire cross-section of the duct. It is expediently arranged such that its movable crushing jaw is disposed on an outer side of the duct, while the stationary crushing jaw is facing that cross-section of the duct which guides the hot air. This has the advantage that the drive elements for the movable crushing jaw can be situated outside the hot region and be accessible for maintenance. The devices for adjusting the outlet gap are usually provided on the crushing jaw which is stationary during operation. According to the invention, however, provision may be made for said devices also to be associated with the movable crushing jaw, in order to be able to make use of the advantage of arrangement in a cooler region for the adjusting devices also.
To ensure that the operation of the furnace and cooler is not endangered in the case of crusher breakdown and that the crusher does not have to be operated in certain operating situations (for example during no-load operation of the furnace in the cold state), the crusher gap should be adjustable to a size such that it permits the passage of the uncrushed material. In addition, provision can be made for at least the movable jaw of the crusher, but preferably the entire crusher, to be removable from the clinker discharge duct in order to be able to open the duct cross-section or to carry out maintenance work on the crusher.
Finally, provision can be made for a shear strip to be disposed at the bottom end of one crushing jaw, under the crusher outlet gap, in order to cover the outlet gap, at a predetermined distance therefrom, during the working stroke.
The crusher to be used in the context of the arrangement according to the invention may have a different configuration from the conventional crushing jaw shapes, even if its function is one typical of the latter. For example, the movable jaw may be formed by a rotatably mounted roll.